Scavenging and Turbocharging

Scavenging and turbocharging

Q: During normal engine operation a turbocharger rapidly loses speed and the speed reduction is accompanied by appreciable noise. (a)State with reasons the possible causes.

The two factors of loud noise and rapid speed reduction indicates that rotational friction has dramatically increased, or the rotor is in contact with the stator, which could be due to

◊Bearing failure: Bearing failure will affect the rotor clearances, causing the rotor to contact the stator.

Bearing may fail due to Lack of lubrication

– Dirty lubricant

– Lack of cooling

– Excess vibration

– Failure due to fouling

– Failure of the resilient mounting

– Over running hour.

– Faulty sealing system.

◊Mechanical damage to the rotor:

If any component from the combustion chamber is admitted to the exhaust side of the rotor, the rotor will be imbalanced and may leading to possible bearing failure.

◊Failure of the water coolant casing: This will admit water to the gas inlet and cause a reduction in the rotor speed

b. State with reasons the factors which may limit engine operating speed with the turbocharger out of operation

Ans: The exact power limit with a defective turbocharger will depend upon the actual configuration of the system and how many turbochargers remain in operation

The following factors need to be considered when operating the engine:

◊Exhaust temperatures: The actual operating conditions should be taken into consideration and engine manual would be consulted as to the maximum limit

◊Exhaust smoke levels: Exhaust color should be monitored. Allowance should be made for the change of rate acceleration to prevent excessive thermal load.

◊Maximum engine power: This will be limited due to the factors stated above, and this will probably be approximately 50% power with the loss of one of the two turbochargers. Hence the engine power would be reduced in consideration with all the above factors.

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